Intermolecular interactions in biointerfaces: a blueprint for smart responsive materials

This work explores some fundamental yet often overlooked aspects of physicochemical interactions, such as intermolecular ones. In this framework, we begin by examining simple systems followed by more complex biointerfaces to obtain key insights, which are then applied to the design of smart, autonomous, multiresponsive soft materials. We began by examining the diffusion and aggregation behaviour of a prominent green solvent, glycerol carbonate (GC) in water, confirming its self-aggregation. Next, we explored the spectral properties of the bromothymol blue (BTB) dye in aqueous solution, focusing on the effects of electrolytes, hydrogen bonding (by varying H2O:D2O ratio), and degassed water. Our findings showed that each factor significantly impacts the dye’s spectral properties and its self-aggregation behaviour. Then, we investigated the influence of molecular geometry in polyatomic ions by studying sodium halates. We measured or calculated physicochemical properties such as polarisability, partial molar volumes, Jones-Dole B coefficients, and limiting conductivity. These showed that the unique molecular geometry of each halate caused a high polarisation anisotropy, reversing the Hofmeister trend compared to their halide counterparts and giving iodate ion a strong kosmotropic character. In the second part, we shifted our focus to biointerfaces, recalling the findings and conclusions from the first part. We began by investigating the effect of adding electrolytes to aqueous urease solutions, observing the resulting changes in enzymatic activity. Both cations and anions were studied, revealing distinct mechanisms unique to each ion. We also examined the effects of H2O:D2O ratio and dissolved gases to further extend the insights gained from the first part of the study. Next, we investigated a peptide-based system, that serves as a versatile platform for developing multiresponsive gels with customisable properties. We selected an amyloidal decapeptide fragment, ACP(65-74)-NH2. An extensive study was conducted on its gels, focusing both on the effect of solvents choice and the presence of different counterions. Both water and GC were used as solvents to examine the effects of different solvent environments. We showed that the unique nature of the solvent changes amyloid fibrillation and morphology, but also the resulting rheological properties. Additionally, we studied the effect of post-synthesis counterions using trifluoroacetate, chloride, bromide, iodide and sulfate. The results revealed significant changes in the gel properties, amyloidogenesis, and morphology, depending on the ion used. Finally, these insights were used in preparing responsive soft materials: i) we physically entrapped urease in a gellan/mucin biopolymer mixture to create a multiresponsive material. This material was then applied as a means to design chrono- and pH-responsive hydrogel, and as a template for oscillatory reactions. ii) ACP(65-74)-NH2 gels were characterised. We found that all gel samples possess pH responsiveness with fully reversible sol-to-gel transitions, except for the gels containing bromide. The samples had typical shear-thinning behaviour and the rheological properties were found to be dependent on the temperature. The temperature dependence of the gels in water showed a peculiar behaviour that is similar to that of thermoresponsive polymer solutions.